The objective of the present proposal is to attempt complementation of molecular defects in cells cultured from patients with Xeroderma pigmentosum (XP). XP is a skin disease associated with defects in DNA metabolism, particularly in DNA repair of sunlight-induced damage. These studies will be aimed at using the excision repair uvr genes (uvrB and uvrC) of Escherichia coli to complement the basic defects of excision repair in XP cells. In particular, gene transfection methods will be employed to carry out the proposed studies. The well characterized repair genes will be placed downstream from the promoter sequences in eukaryotic expression vectors. Two types of expression vectors will be used: the avian tumor virus long terminal repeats (LTR) and the Simian virus (SV40) vectors. Cells from various complementation groups of XP will be used to ensure wide test-range for counterpart E. coli repair genes. The proposed studies will allow direct comparison of DNA repair mechanisms both in prokaryotes and eukaryotes. These studies will help in elucidating the mechanism(s) of expression of genes in foreign environments.